Semiconductor processing comprises a complex series of sequential steps through a number of semiconductor processing tools adapted to perform various operations. Such operations include, but are by no means limited to, photoresist deposition, exposure, and development; etching; deposition of conductive and dielectric layers; and planarization. Often, a single wafer may undergo the same operations multiple times as each layer of circuit design is created. Frequently, it is desirable to clean the wafer to reduce interfacial contamination before certain process steps. Such cleaning may comprise exposing the wafer surface to reactive ion plasma or to other cleaning gases.
Wafer cleaning steps may be ex-situ or in-situ. An ex-situ cleaning step is one in which the wafer is cleaned in one process tool before the main processing occurs in another processing tool. Ex-situ cleaning may have certain disadvantages, including the potential for recontamination between the cleaning step and the next processing step. In this case, a limited time window between the cleaning step and the next processing step is required. An in-situ cleaning step is one in which the wafer is cleaned in the process tool which performs the main processing step. The existing art for in-situ cleaning of wafers requires placing the wafer in a fixed separate chamber or a fixed position within a transfer chamber. Such a separate chamber increases the cost, the processing time, and the space dedicated to the tool.
During cleaning, a wafer is typically placed on a chuck or similar support that keeps the wafer stationary while processing occurs. To accommodate the support, the chamber in which the wafer is cleaned is typically at least as wide and deep as the wafer diameter. The wafer is typically handled before cleaning to set it in place for the cleaning step which is to be performed and again after cleaning to remove the wafer from the chamber. In-situ cleaning offers the benefit of a cleaner and more controlled wafer surface as compared to ex-situ cleaning.
Other wafer cleaning processes or chemical treatment processes such as sputtering or vapor deposition are also typically performed in chambers that are at least as large as the wafer, in which the wafer remains stationary during treatment, and in which the wafer is typically handled to place and remove the wafer. There is a need in the art, therefore, for a more compact apparatus, especially one with reduced dimension in the direction of wafer movement. A related need is for an apparatus that permits plasma cleaning of wafers while the wafer is in transit from the load area to the main processing area.